1. Field of the Invention
The present invention describes an efficient method for assaying nucleic acids employing fluorescence.
2. Related Art
In medical and biological fields, a DNA or RNA probe complexed with a radioactive isotope has been employed as a means of detecting nucleic acids. This technique comprises hybridizing the labeled probe with a target nucleic acid, followed by detecting the target nucleic acid by autoradiography. This isotope method has numerous drawbacks which are serious obstacles to the application and development of this technology. The drawbacks of the isotope method are as follows:
(a) The nucleic acid hybridization method lacks spatial resolution sufficient to reveal the relative positional relationship between contiguous signals. PA1 (b) Experimental procedures using isotope can only be performed in isotope laboratories equipped with special facilities. This hinders the application of the hybridization method, particularly for clinical applications. PA1 (c) Use of isotope is dangerous for laboratory workers even under controlled laboratory conditions. In addition, a danger for non-laboratory workers also exists because of radioactive wastes. PA1 (d) An extended period (several weeks to several months) may be required for detection, such that application to rapid clinical diagnosis is difficult. PA1 (e) Radioactivity decays with a definite half-life period. Accordingly, experiments must be scheduled around a purchase date of isotope. If the schedule chart is slightly altered, there is a danger of wasting isotope or experimental results on a large scale. PA1 (f) To enhance detection sensitivity, significant quantities of radioactivity must be incorporated in a nucleic acid probe. However, this highly radioactive nucleic acid is unstable and easily suffers from radioactive disintegration. PA1 (g) In general, isotope is extremely expensive. This prevents general use of the hybridization method.
In view of such drawbacks, DNA or RNA labeling methods in place of employing radioactive isotope have been developed. For example, BLU GENE KIT.TM., commercially available from Bethesda Research Laboratories Inc. (BRL Inc.), is known. Additionally, "Nucleic Acid Probe And Use Thereof" is disclosed in Japanese Patent Application Laid-Open No. 60-226888.
However, these techniques do not eliminate all of the drawbacks described above. In particular, detection sensitivity is not comparable to that of the isotope method. In the above labeling, the detection sensitivity is "10.sup.-12 g DNA," slightly inferior to the "10.sup.-13 g DNA" of the isotope method.
An object of the present invention is to provide a method for assaying nucleic acids which eliminates the drawbacks of the isotope method and which also provides excellent detection sensitivity.